Process of improving collagen by removing fat therefrom



3,532,593 PROCESS OF IMPROVING COLLAGEN BY REMOVING FAT THEREFROM Harland H. Young, Western Springs, 11]., assignor t Swift & Company, Chicago, 11]., a corporation of Delaware No Drawing. Filed Feb. 1, 1966, Ser. No. 523,871 Int. Cl. D01c 3/00 U.S. Cl. 1622 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for preparing a fatfree collagen from a cured collagen wherein the pH of comminuted fibrous protein materials is lowered to about 4.5 or lower at a temperature not in excess of 40 C. The material is cured at this pH until translucent, and then mechanically worked by beating until a gel is obtained. The gel is diluted to less than 5% solids and agitated to encourage flotation of fat which is skimmed from the solution.

In general, the present invention relates to an improved paper product containing collagen, and to an improved collagen useful therein.

In the preparation of paper, raw chemical pulp is first broken up by rough mechanical treatment, or otherwise, and suspended in water. In order to render the rough suspension suitable for formation into paper it is then subjected to a further processing wherein the pulp is subjected to the action of cones, discs, serrated rollers or the like, to effect the proper hydration of the cellulose and the proper freeness (strainability) of the fibers. The extent of this latter treatment will, of course, depend to a large degree upon the type and strength of the paper to be formed.

During or after this latter refining process, various additives are ordinarily incorporated into the mixture in order to impart desired characteristics, such as freeness, water retention, strength (wet and dry), specific surface, adsorption capacity and specific volume, to the final product. Additives suitable for these purposes include rosin size, alum, starch, proteins, clays, pigments and various additives which affect the beating rate and, as a result, the properties of the final paper.

More recently, it has become a practice to incorporate various fibers, for example, glass, nylon, dacron and numerous cellulose esters into the paper pulp during the final processing step. As these materials are themselves nonbonding, various resins and adhesives are usually incorporated with these fibers to effectively bond them into the final product.

Although papers prepared by the aforementioned method are usually satisfactory there is a continuing need in the industry for improved paper having the previously stated properties which may be economically produced.

Therefore, it is an object of the present invention to provide an improved paper product having desirable surface properties and improved wet and dry strength.

It is a further object to provide a paper product in which no additional bonding resins or adhesives are required.

It is another object to provide an economical method for preparing an improved paper product.

It is yet another object to provide an improved collagen suitable as an additive to paper products.

It is still another object to provide an improved method for purifying collagen.

Additional objects if not specifically set forth herein will be readily apparent to those skilled in the art from the following detailed description of the invention.

nited States Patent "ice 3,532,593 Patented Oct. 6, 1970 It has been found that a highly desirable product may be attained by the addition of collagen to paper pulp in a particular manner.

Various additives have been combined with paper pulp in an attempt to prepare desired products. These conventional materials include vegetable gums, starch, animal glue, carboxy methyl cellulose, casein and soy protein. Such materials serve not only to bond other additives into the final product, but, in many instances, also serve as sizing or bonding agents. Many of the aforementioned additives are undesirable to an extent in that they tend to retard or interfere with the beating of the pulp. For this reason, they are frequently added just prior to sheet formation, and, as a result, may be unevenly dispersed throughout the pulp. Furthermore since these materials are water soluble, considerable quantities are lost through the paper machine Wire or screen. In addition, these materials tend to transfer to the felt resulting in a buildup on the felt surface.

Collagen, on the other hand, does not retard or interfere with the beating of the pulp, and, being insoluble in cold water, is not lost through the paper screen or onto the felt. However, collagen retains the advantages of the above materials in that it both retains other additives in the paper as well as imparting desirable properties itself.

In general, the method employed in the present invention comprises mixing a cured acidified collagen with paper pulp in a ratio of from about 1:200 to about 1:10, and preferably 1:100 to 1:20; adjusting the pH of the mixture to below about 4.5, and preferably 2.5 to 3.5; beating the mixture until the collagen is hydrated and dispersed throughout the pulp; forming a sheet of the dispersed material; and heating the sheet thus formed to partially gelatinize said collagen.

As an alternative to the above method, it is possible to acidulate the collagen and form a collagen gel prior to combining the collagen with the paper pulp. It is also possible to prepare a product which is superior in many respects by adjusting the pH to above about 6 and preferably about 6.5 to 7.5 just prior to sheet formation. By this pH adjustment, collagen fibers are regenerated from the gel, and said fibers, because of the uniform dispersion of the collagen gel within the paper pulp, are themselves uniformly dispersed and intertwined with the cellulose.

As shown above, the sheet of paper material is heated after sheet formation. Such heating is generally at least about 60 C. and preferably from about to about C. This heating step partially gelatinizes the collagen present in the sheet material and the gelatin thus formed acts as a binder for the paper, collagen and rernaining materials in the sheet. In this manner, it is possible to utilize the binding properties of gelatin without experencing the difiiculties heretofore encountered through loss of gelatin from the mixtures during sheet formation.

It will, of course, be understood that other additives besides collagen and paper pulp may be used in preparing the present products. These additives will be readily apparent to one skilled in the art and include rosin size, alum, starch, proteins, clays, pigments, and other materials including those previously described in this specification. Furthermore, by the present process, various crosslinking or tanning agents such as aldehydes, heavy metal salt, and cyanamide may be reacted with the paper sheet in order to produce a moisture resistant paper when the surfaces of the paper have been heated. These crosslinking agents may be introduced into the head box, on the wire, on the belt, or just prior to the last squeeze roll.

Collagen prepared by a variety of methods is applicable in the present invention so long as the collagen used is of a reasonable degree of purity. As is Well known, collagen is the white fibrous protein constituent of connective tissue and is one of the most abundant of animal proteins. Richest sources of the protein are the hides, skins, sinews and bones, although bones are less preferred as a source of the fibrous protein. Fibrous collagen is readily available by merely macerating hides, skins, sinews or other connective tissue. The crude fibrous protein obtained by macerating of the above materials comprises variable quantitives of fat or some adipose tissue which, is highly difficult to remove. In order that collagen is suitable for incorporation into paper, the excessive quantitives of fat must be removed in order to avoid spotting, random grease spots or fish eyes.

In the past, various methods have been employed in order to remove the fat from collagen material. However, these prior methods inherently result in certain undesirable effects. For example, solvent extraction or wet and dry rendering have been attempted, but these methods also result in undesirable denaturization and degradation of the native collagen protein. Special extraction methods employing such materials as acetone which simultaneously dehydrate and degrease the fibrous protein material are in most instances prohibitively expensive.

As a part of the present invention, a method for obtaining substantially complete removal of the undesirable fat from collagen materials without the inherent undesirable features heretofore experienced has been discovered. Briefly, this process comprises first the lowering of the pH of comminuted fibrous protein materials such as dehaired and fleshed hides or skins as well as sinews to a pH of about 4.5 or lower at a temperature not in excess of 40 C. The material thus treated is then held at the lower pH until a uniform cure is obtained as indicated by the translucency of material. The cured material is then mechanically worked by intensive beating, shearing or grinding until a translucent gel is obtained. The acidulated gel is then diluted while still maintaining the temperature at below 40 C. to a point where it is pourable; preferably at this time the gel contains less than about 5% solids. The diluted gel is then mechanically worked and agitated to encourage flotation of the fat. At this point, the gel may optionally be treated with a basic material in order to increase the pH to at least 6.0 in order to precipitate collagen fibers and release additional fat. Either after the preceding step or the previous mechanical working the cold fat butter is easily skimmed because no emulsification takes place below the melting point of the fat. The pH of the gel is reacidulated to the pH of 4.5 or below prior to its addition to the paper pulp. This latter step is unnecessary in the event that the pH was not increased during the above process. If it is desired to ship or store the material for a period of time prior to mixing with the paper pulp and additives, the material may be preserved by subjecting it to dry salt, brine, or other form of preservation.

As stated above, the process of the present invention should be conducted at a temperature of below about 40 C. However, it is desirable to use even lower temperatures of about C. and preferably 20 C. or lower in order to obtain the optimum results. In order to lower the pH in the above process, all mineral and organic acids and their acid salts may be used so long as the pH is maintained below about 4.5 and the saline concentration is insuificient to impede swelling and dispersion. For this purpose, it is preferred from the standpoint of economy that hydrochloric acid be used, although sulfuric, sulfamic, lactic, phosphoric and other acids are equally suitable.

At the lower pH and lower temperature ranges, the fat butter is released in solid non-emulsified form and, as a result, is easier to remove by skimming. In order to obtain adequate fat removal by the above process, the diluted gel should be of a percent solid concentration of below about 5%, and preferably about 2% collagen solids.

In plant operation, it is possible to combine the above process with the paper making process by simply combining the purified collagen formed by the above method with the paper pulp and other additives. In this manner, it is possible to employ conventional pulp beating equipment for the gel preparation process.

The following examples of the collagen purification process and paper preparation are presented for the purpose of illustration only and are not to be construed as limiting the scope of the invention.

EXAMPLE I Hide trimmings obtained from the removal of shanks, pates and belly edges from fleshed hides were depilated by soaking in 3 molar ammonium hydroxide and running through a dehairing machine. The hide pieces were then washed in a tannery wheel with cold water (18 C.) until ammonia was no longer detected by odor. The washed stock was then soaked in three times its weight of water containing 0.8% anhydrous hydrochloric acid basis hide stock at temperatures of l518 C. with occasional rotation of the wheel for agitation. After 16 hours of cure the stock was washed with one change of water and transferred to a Hollander paper pulp beater with suflicient water to produce a total collagen solids of approximately 2%. The beater was started and every 15 minutes the pH was checked and adjusted to 2.8-3.2 with hydrochloric acid. After the first acid addition, fat butter began to collect in back of the bafile plate on the entrance side of the beater wheel and could be removed at intervals as a white solid butter. After 1.5 hours beating with intermittent skimming the collagen was a semi-gel having almost crystal clarity and moved slowly around the beater trough with no more separation of the fat. The pH at this time was 3.0 and the temperature had risen to 26 C. The material was then neutralized with sodium hydroxide and the collagen reformed as a fibrous mass which was removed by running through a rotating screen washer. It was further dehydrated by mixing with a dry salt and draining until the total shrink was 23% in which condition it could be stored for several months at ambient temperature.

EXAMPLE II Pickled skins prepared from sheep skins by soaking in 15% sodium chloride brine containing 1.5% sulfuric acid were washed until plumping had reached a maximum indicating efficient salt removal. Additional sulfuric acid was then added to produce a pH of 2.5 and the skins were permitted to cure at 12 C. for 12 hours. Excess salt and acid were removed by continuously rotating in a tannery wheel at 12l6 C. for 8 hours. The plumped skins were then ground into shreds in an Urshel Cutter and dispersed in sufiicient water to yield a solution of 3 solids. This slurry was then run in a Hollander beater with the pH adjusted to 3.8-4.0. After 2 hours and 45 minutes the fat butter no longer appeared back of the baffle and the semi-fluid gel was substantially clear and free from opaque pieces. Traces of hair were then removed by forcing the semi-gel through a 20 mesh screen. The final clear gel was adjusted to pH 4 and was ready for use as a pulp beater additive. This final material contained less than 2% fat content basis dry solids and could be cast into clear films having a definite fibrous structure.

EXAMPLE III Eight hundred grams of drained bashed pork skins were were suspended in 9,000 grams of cold water containing 12 grams of hydrochloric acid (37%). This material was placed in a Hollander pulp beater and the beater was started. After 15 minutes, fat butter began to accumulate behind the baflle plate. Skimming was effected intermittently and at the end of 3 hours beating, 300 grams of fat butter represented a yield of about grams of pork fat dry or approximately 22% basis raw skins after fleshing. The clear beaten semi-fluid gel had a pH of 3.7. The gel was then neutralized by adding directly to the beater 25 grams of 29% ammonium hydroxide over a period of about 15 minutes. At the end of this addition, the mass was fibrous suspension of opaque collagen which was chilled during formation to 8 C. by the addtiion of ice. The fibrous mass was then removed and washed with ice water on a revolving screen until free of ammonium salt. The collagen was then squeezed dry and frozen until needed. The fat content dry basis of this material was about EXAMPLE IV Approximately 1,000 grams of green sinews and pizzles from cattle were held in a 10 C. solution of 5,000 grams of Water and grams concentrated hydrochloric acid for 24 hours. This cured stock was then macerated with an Urshel Cutter until a stiff opaque gel was obtained having approximately 10% solids and a pH of 1.82.2. Analysis indicated a fat content dry basis of 16%. The pasty gel was then worked into a semi-fluid gel of about 2% solids by vigorous agitation with a lightning mixer and diluted further to less than 1% solids and agitated mildly as it passed through a fat recovery basin wherein it was subjected to aeration with compressed air causing the fat to float as butter which was removed by intermittent skimming. After removal from the fat recover zone, the fluid gel was neutralized to a pH of 6.0-6.8 using metered lime water. The fibrous collagen thus precipitated was screened and washed with cold water until free of calcium salts and was further dehydrated and preserved by dry salting and draining.

EXAMPLE V Kraft pulp previously beaten until ready for sheet formation was cooled to 60 F. and was mixed with 3% basis pulp solids of acid cured beaten collagen gel from Example 1. The mixture was then beaten for 30 minutes and finally diluted to 0.5% consistency. This material was then formed into paper sheets which were dried between Teflon screens and hot platens at a temperature of 121 C., resulting in a smooth, almost glazed, strong paper.

EXAMPLE VI The procedure of Example V was conducted with the exception that the sheets were lightly sprayed with a 1% formaldehyde solution prior to drying. The paper thus formed exhibited much greater wet strength than the paper prepared in Example V, and was equivalent in other respects.

EXAMPLE VII Five hundred grams of the cured collagen beaten gel prepared in the manner of Example III was added to 250 grams of cellulose beaten pulp (dry basis) and then dispersed in 5,000 grams in cold water. A uniform pulp slurry resulted after beating of this mixture for 15 minutes at a pH of 3.8. This material was divided into two portions. The first portion was formed into a sheet and dried between hot platens at a temperature of 110 C. The second portion was combined with 1% of hexamethylene tetra amine basis collagen protein. After 15 minutes reaction time, the sheet was felted, cold pressed and dried between the hot platens. The sheet resulting from the treatment of this second portion exhibited improved wet strength in comparison with the untreated sheet prepared from the first portion.

EXAMPLE VIII Collagen-cellulose beaten pulp prepared in the manner of Example VII was combined with 1% of water soluble phenol formaldehyde and urea formaldehyde resins basis dry collagen. This material, when formed into sheets which were dried on hot platens, resulted in extremely strong sheets having excellent wet strength.

EXAMPLE IX Collagen-cellulose beaten pulp prepared in the manner of Example VII was combined with 15% basis pulp of nylon fibers. After dispersion of the nylon fibers, the pH of the mixture was adjusted to pH 6, resulting in regeneration of the collagen fibers. Sheets prepared from this mixture showed excellent retention of the nylon fibers which were uniformly dispersed through the sheets.

The following table illustrates the relative tensile strength of various paper products in comparison with the products of the present invention. Tensile strength is expressed in pound pull to break per inch at constant thickness.

10 TABLE I Composition: Tensile strength, lbs. Paper (no additives) 21 Paper plus 6% cured collagen 40 Paper plus 6% gelatin 17 Paper plus 6% leather 16 The following table is for the purpose of illustrating the effects of various levels of cured callogen paper both wet and dry on the Mullen (burst) test and tensile strength. Tensile strength is again expressed in pounds pull to break per inch at constant thickness. The Mullen is expressed in pounds per square inch pressure on the oil forcing the inflation.

TAB LE II Mullen test; Tensile strength Wet Dry Wet Cured, percent collagen Dry Obviously, many modifications and variations of the present invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for preparing an improved collagen from a cured collagen material comprising: lowering the pH of said material to below about 4.5 and the temperature of said material to below about 40 C.; forming a translucent gel of said material; diluting said gel to form a solution of less than about 5% solids; agitating the solution to encourage flotation of fat; adjusting the pH of the solution to above about 6.0 to release additional fat; and skimming said fat from said solution.

References Cited UNITED STATES PATENTS 2,934,446 4/1960 Highberger et a1. 162-2X 2,934,447 4/ 1960 High'berger et al. 1622 X 3,223,551 12/1965 Tu 117-14o 3,294,579 12/1966 Tu 162144X 3,294,581 12/1966 Hervey et al. 162144 x 3,394,047 7/1968 Sommer et al. 162 1s7 OTHER REFERENCES Casey, Pulp and Paper N.Y. Interscience Pub. Inc. 1960, vol II, p. 947.

HOWARD R. CAINE, Primary Examiner US. Cl. X.R. 

